Preclinical Study of Radiolabeled LyP-1 for Detecting Sunitinib-induced Changes in the Tumor Microenvironment and Synergistic Antitumor Effects in Triple-negative Breast Cancer.

[PURPOSE] Sunitinib is an anti-angiogenic drug that can induce drug resistance characterized by hypoxia. We aimed to synthesize two novel radiolabeled LyP-1 peptides, Tc-HYNIC-LyP-1 and I-LyP-1, to detect sunitinib-induced changes in the tumor microenvironment and improve the therapeutic effects in triple-negative breast cancer (TNBC) mice models.

[METHODS] We synthesized Tc-HYNIC-LyP-1 using hydrazinonicotinamide (HYNIC) as the chelating agent and labeled the LyP-1 peptide with I using the chloramine-T method to synthesize I-LyP-1. Radiochemical purity and stability of the peptides were assessed in vitro using thin-layer chromatography. Tumor accumulation and biodistribution of Tc-HYNIC-LyP-1 were measured in 4T1 xenografts with or without sunitinib treatment. Immunohistochemical analysis was performed to detect sunitinib-induced changes. The therapeutic potential of I-LyP-1 alone and in combination with sunitinib was evaluated in a TNBC mouse model.

[RESULTS] Tc-HYNIC-LyP-1 and I-LyP-1 could be readily prepared with satisfactory labeling efficiency (95.4% ± 0.6% and 72.5% ± 4.5%, respectively) and stability (both more than 90%) in vitro. Micro-single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging of mice transplanted with 4T1 tumors using Tc-HYNIC-LyP-1 demonstrated that the uptake of this probe was high in 4T1 xenografts treated with sunitinib at 90 min, whereas it was mild in the control group. Semiquantitative analysis of the ratio of radioactivity intensity at tumor site to that of adjacent muscles (T/M value) showed that the average T/M value of the sunitinib treatment group at 90 min was 3.27, while it was 0.91 in the control group (p = 0.0022). I-LyP-1 could significantly inhibited tumor growth with good organ compatibility and had a synergistic therapeutic effect when combined with sunitinib, with an approximately threefold reduction in the tumor volume in comparison with the control group CONCLUSION: Micro-SPECT/CT imaging using Tc-HYNIC-LyP-1 can be used to monitor sunitinib-induced changes in the TNBC tumor microenvironment. The combination of I-LyP-1 and sunitinib may serve as a novel treatment for TNBC.